Early expression of glycophorin C during normal and leukemic human erythroid differentiation

Glycophorins C and D (GPC and GPD) are two erythrocyte glycoproteins which originate from the same gene but differ in their NH2-terminal residues. The cell surface expression of these glycoproteins during normal and erythroid differentiation has been investigated with monoclonal and polyclonal antibodies and has been compared to the expression of glycophorin A (GPA), the major sialoglycoprotein of human red cells. Using glycosylation-independent antibodies (monoclonal or polyclonal), GPC or GPD was detected in erythroid and nonerythroid cell lineages. However, a glycosylation-dependent monoclonal antibody (MR4-130) detected an epitope on GPC which appears to be erythroid specific, suggesting that lineage specificity of this glycoprotein is related to some carbohydrate structures. During normal erythroid differentiation, GPC was expressed early at the level of erythroid progenitors (part of erythroid burst-forming unit and erythroid colony-forming unit) as detected with a glycosylation-independent monoclonal antibody (APO 3), whereas GPA is only present during terminal erythroid differentiation. The MR4-130 epitope was not coordinately expressed on the cell surface with the GPC molecule in the erythroid differentiation, since it was detected at the level of the more mature erythroid colony-forming unit slightly later than the GPC polypeptide. In four erythroleukemic patients, blast cells blocked at discrete stages of the erythroid differentiation were also investigated with antibodies and complementary DNA probes for GPA and GPC. GPA was immunologically detected in three of four cases, and its cell surface expression was correlated with the amount of specific mRNA in the cells, as seen by Northern blot analysis. GPC was immunologically detected on the blast cells of all four patients. However, in two cases including one with positive expression of GPA, the MR4-130 epitope was absent from the GPC molecule. By Northern blot analysis, we found that the GPC/GPD mRNA was present at a high level in all four patient samples. Western blot analysis of GPC and GPD in two of these patients revealed that these mRNAs were mostly translated into the GPD molecule, suggesting that these glycoproteins might be differently processed in certain cases of erythroleukemia.